A study of the personal income distribution in Australia

We analyze the data on personal income distribution from the Australian Bureau of Statistics. We compare fits of the data to the exponential, log-normal, and gamma distributions. The exponential function gives a good (albeit not perfect) description of 98% of the population in the lower part of the distribution. The log-normal and gamma functions do not improve the fit significantly, despite having more parameters, and mimic the exponential function. We find that the probability density at zero income is not zero, which contradicts the log-normal and gamma distributions, but is consistent with the exponential one. The high-resolution histogram of the probability density shows a very sharp and narrow peak at low incomes, which we interpret as the result of a government policy on income redistribution.Comment: 7 pages, 4 figures, Proceedings of the Econophysics Colloquium, Canberra, 14-18 November 200

Continuous Chiral Transition in Strongly Coupled Compact QED with the Standard Torus Topology

We analyze the phase diagram of compact QED on the torus with a chirally symmetric four fermion interaction added to the usual Wilson action. Inside a mean field approximation for the four fermion term, a line of first order phase transitions and another one of second order are found in the $(\beta, G)$ plane. Approaching the second order line a continuum limit can be defined. Critical exponents vary along this line in a similar way as in the non-compact model, suggesting that a non trivial interacting continuum theory can be constructed.Comment: 11 pages, latex, 1 figur

Nature of the phases in the frustrated XY model on the honeycomb lattice

We study the phase diagram of the frustrated XY model on the honeycomb lattice by using accurate correlated wave functions and variational Monte Carlo simulations. Our results suggest that a spin-liquid state is energetically favorable in the region of intermediate frustration, intervening between two magnetically ordered phases. The latter ones are represented by classically ordered states supplemented with a long-range Jastrow factor, which includes relevant correlations and dramatically improves the description provided by the purely classical solution of the model. The construction of the spin-liquid state is based on a decomposition of the underlying bosonic particles in terms of spin-1/2 fermions (partons), with a Gutzwiller projection enforcing no single occupancy, as well as a long-range Jastrow factor.Comment: 9 pages, 6 figures, 3 table

Spiral antiferromagnets beyond the spin-wave approximation: frustrated XYXY and Heisenberg models in the honeycomb lattice

We examine the stability of classical states with a generic incommensurate spiral order against quantum fluctuations. Specifically, we focus on the frustrated spin-1/2 $XY$ and Heisenberg models on the honeycomb lattice with nearest-neighbor $J_1$ and next-nearest-neighbor $J_2$ antiferromagnetic couplings. Our variational approach is based on the Jastrow wave functions, which include quantum correlations on top of classical spin waves. We perform a systematic optimization of wave vectors and Jastrow pseudo-potentials within this class of variational states and find that quantum fluctuations favor collinear states over generic coplanar spirals. The N\'eel state with ${\bf Q}=(0,0)$ extends its stability well beyond the classical value $J_2/J_1=1/6$. Most importantly, the collinear states with ${\bf Q}=(0,2\pi/\sqrt{3})$ (and the two symmetry-related states) are found to be stable in a large regime with intermediate frustration, while at the classical level they are limited to the point $J_2/J_1=0.5$. For large frustration, the $120^\circ$ state is stabilized for finite values of $J_2/J_1$ in both models.Comment: 10 pages, 10 figures, 4 table

Self-organized partitioning of dynamically localized proteins in bacterial cell division

The Min proteins are equally partitioned between daughter cells at division.The mechanism allowing this accurate distribution is intrinsic to the Min system.Individual oscillations appear in each daughter cell before cytokinesis is completed.Diffusion through the gradually constricting septum is key to this process

Role of ROS and RNS Sources in Physiological and Pathological Conditions

There is significant evidence that, in living systems, free radicals and other reactive oxygen and nitrogen species play a double role, because they can cause oxidative damage and tissue dysfunction and serve as molecular signals activating stress responses that are beneficial to the organism. Mitochondria have been thought to both play a major role in tissue oxidative damage and dysfunction and provide protection against excessive tissue dysfunction through several mechanisms, including stimulation of opening of permeability transition pores. Until recently, the functional significance of ROS sources different from mitochondria has received lesser attention. However, the most recent data, besides confirming the mitochondrial role in tissue oxidative stress and protection, show interplay between mitochondria and other ROS cellular sources, so that activation of one can lead to activation of other sources. Thus, it is currently accepted that in various conditions all cellular sources of ROS provide significant contribution to processes that oxidatively damage tissues and assure their survival, through mechanisms such as autophagy and apoptosis

Can a microscopic stochastic model explain the emergence of pain cycles in patients?

A stochastic model is here introduced to investigate the molecular mechanisms which trigger the perception of pain. The action of analgesic drug compounds is discussed in a dynamical context, where the competition with inactive species is explicitly accounted for. Finite size effects inevitably perturb the mean-field dynamics: Oscillations in the amount of bound receptors spontaneously manifest, driven by the noise which is intrinsic to the system under scrutiny. These effects are investigated both numerically, via stochastic simulations and analytically, through a large-size expansion. The claim that our findings could provide a consistent interpretative framework to explain the emergence of cyclic behaviors in response to analgesic treatments, is substantiated.Comment: J. Stat. Mech. (Proceedings UPON2008

New proposal for numerical simulations of systems with a theta-vacuum term

A new approach to perform numerical simulations of systems with a theta-vacuum term is proposed, tested, and applied to CP3 The main new ingredient of this approach is the method used to compute the probability distribution function of the topological charge at theta=0. We comment also on the possibility of applying this approach to QCD at finite baryon density.Comment: Talk given by Vicente Azcoiti at the Lattice 2002 Symposium (Algorithms